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The muscular composition of worms varies depending on their type. Flatworms, for example, have a layer of circular muscle fibres under the epidermis, a layer of diagonal fibres, and a deeper longitudinal layer. They also have dorsoventral muscle fibres running from the upper to the lower epidermis of the flattened body. Roundworms, on the other hand, have obliquely striated, longitudinal muscles but no circular muscles. They are enclosed in a thick cuticle that allows bending but prevents swelling. Most worms have two bands of muscles: longitudinal muscles that run the length of the body and circular muscles that form circular bands around the body.
| Characteristics | Values |
|---|---|
| Muscle structure | Most worms have two bands of muscles: longitudinal muscles that run the length of the body and circular muscles that form circular bands around the body. |
| Flatworms | Have a layer of circular muscle fibres immediately under the epidermis, a layer of diagonal fibres, and a deeper longitudinal layer. Dorsoventral muscle fibres run from the upper to lower epidermis. |
| Roundworms | Have obliquely striated, longitudinal muscles but no circular muscles. |
| Nematodes | Only have longitudinal muscles. |
| Annelids | Have both circular and longitudinal muscles. |
| Earthworms | Have circumferential and longitudinal muscles edging each segment. |
| Muscle function | Contraction of the circular muscles makes the worm longer and narrower, while contraction of the longitudinal muscles makes the worm shorter and fatter. |
| Movement | The circular and longitudinal muscles work together to produce the crawling movement of worms. Nematodes, which only have longitudinal muscles, move by contracting these muscles and wriggling forward. |
| Reflexes | Touching an earthworm stimulates the subepidermal nerve plexus, which connects to the intermuscular plexus and causes the longitudinal muscles to contract. This results in the writhing movements observed when a human picks up an earthworm. |
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What You'll Learn
Flatworms have a layer of circular muscle fibres under the epidermis
Flatworms, or phylum Platyhelminthes, are the simplest worms, with most having flattened shapes like leaves or ribbons. They possess a distinct muscular structure, with three primary layers of muscle fibres. Immediately under their epidermis, flatworms have a layer of circular muscle fibres. This circular muscle layer acts in coordination with other muscle layers to enable various body movements.
The circular muscle fibres in flatworms are responsible for the worm's ability to modify its body shape. By contracting these circular muscles, the worm's body becomes longer and thinner. This change in shape is essential for the worm's locomotion, particularly in crawling. When the circular muscles contract, the worm's body elongates, allowing it to push itself forward in a crawling motion.
In addition to the circular muscle layer, flatworms also possess a layer of diagonal fibres and a deeper longitudinal layer. These muscle fibres work in combination to produce different body shapes. For example, when the longitudinal muscles contract, the worm's body becomes shorter and fatter. This ability to adjust their body shape allows flatworms to navigate through their environment effectively.
The muscular system of flatworms also includes dorsoventral muscle fibres that run from the upper to the lower epidermis of their flattened bodies. These dorsoventral muscles play a role in enabling the worm to bend to one side or the other. By contracting specific muscle groups, flatworms can achieve side-to-side movements, enhancing their mobility and adaptability.
The combination of circular, diagonal, longitudinal, and dorsoventral muscle fibres in flatworms provides them with a versatile range of motions. These muscles allow flatworms to crawl, adjust their body shape, and bend to the sides, facilitating their navigation through their surroundings. The presence of these muscle layers showcases the intricate muscular system that enables flatworms to exhibit a variety of behaviours and adapt to their environment.
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Roundworms have longitudinal muscles but no circular muscles
Most worms have two bands of muscles: longitudinal muscles that run the length of the body and circular muscles that form circular bands around the body. However, unlike other worms, roundworms, also known as nematodes, only have longitudinal muscles. This is why they move by contracting the long muscles on either side of their body and wriggling forward, rather than crawling.
Roundworms have obliquely striated, longitudinal muscles but no circular muscles. They are enclosed in a thick cuticle that allows bending but prevents swelling. Therefore, the contraction of the longitudinal muscles can only bend the body up or down (dorsal or ventral). By preventing swelling, the cuticle ensures that shortening one muscle group stretches the other, making the dorsal and ventral longitudinal muscles antagonistic to one another.
Roundworms crawl between soil particles or among the villi of a host's gut by undulating waves of muscular contraction. Similar movements also enable some roundworms to swim. The nervous system of nematodes consists of a set of nerves that run the length of the body and connect to anterior ganglia.
Flatworms, also known as phylum Platyhelminthes, have a layer of circular muscle fibres immediately under the epidermis, a layer of diagonal fibres, and a deeper longitudinal layer. These muscles act in various combinations to make the body long and thin, short and fat, or bent to one side or the other. These muscles are also used by some of the larger flatworms to pass waves of muscular contraction along the body, enabling the worm to crawl in a snail-like fashion.
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Earthworms have circumferential and longitudinal muscles
Earthworms are invertebrates and lack a rigid skeleton. Their body is divided into segments, each of which has a number of setae or small bristles that help them grip the soil as they move.
Earthworms have two sets of muscles: circumferential and longitudinal. The circumferential muscles loop around each segment, and the longitudinal muscles run along the length of the earthworm's body. When the circumferential muscles contract, the earthworm stretches and becomes longer and thinner. The longitudinal muscles then contract, and the earthworm becomes shorter and wider, or it bends from one side to the other, pulling the body forward.
The presence of these two sets of muscles allows the earthworm to move in different ways. The contractions of the circumferential muscles enable the worm to lengthen and push itself forward. On the other hand, the longitudinal muscles allow the worm to shorten very quickly, which can be an attempt to escape from a predator or another potential threat.
The larger dorsal giant axon in earthworms conducts signals rapidly from the rear to the front of the animal. When the rear of the worm is touched, a signal is sent forward, causing the longitudinal muscles in each segment to contract, resulting in the worm's quick shortening. This reflex does not require the CNS and occurs even if the nerve cord is removed.
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Muscles in earthworms' blood vessels pump blood
Earthworms are soft-bodied invertebrates that lack a true skeleton. Their structure is maintained by fluid-filled coelom chambers that function as a hydrostatic skeleton. They have a double transport system, with coelomic fluid moving within the fluid-filled coelom and a simple closed circulatory system.
The circulatory or blood vascular system of an earthworm consists of blood vessels, a heart, capillaries, and blood glands. Earthworms have a closed circulatory system, complete with arteries, veins, and capillaries. The earthworm's blood contains haemoglobin, a red protein that carries oxygen, similar to human blood.
The earthworm's 'heart' is a body-long blood pump vessel that is aided by five ancillary pairs of contracting vessels, each with flap-like valves to help keep the blood circulating in one direction. The blood vessels in earthworms narrow to capillaries, which pick up oxygen through the skin and deliver it to other parts of the body.
The largest blood vessel in the earthworm's body runs mid-dorsally above the alimentary canal from one end of the body to the other. It has contractile muscular walls that are visible from the outside as a dark line through the thin and semitransparent body wall. This vessel has a pair of valves in the front of the septum in each segment, and the direction of blood flow is from posterior to anterior. It contracts and pulsates rhythmically to force blood from the posterior to the anterior side.
In addition to the largest blood vessel, earthworms have other muscular blood vessels that aid in pumping blood. These include the latero-oesophageal hearts, which are thick-walled vessels with valves that allow blood to flow downwards only. There are also lateral hearts, which connect the dorsal and ventral vessels and have four pairs of valves that direct blood flow.
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Earthworms use circular muscles to lengthen and push forward
The anatomy of earthworms is quite fascinating. They have a tube-within-a-tube body plan, with external and internal segmentations. Each segment has small bristles called setae, which help the worm grip the soil as it moves. Earthworms have two types of muscles: circular muscles and longitudinal muscles. The circular muscles loop around each segment, and the longitudinal muscles run along the length of the body.
The circular muscles play a crucial role in the movement of earthworms. When these muscles contract, the segment becomes longer and thinner. This lengthening occurs because the circular muscles are attached to the body wall, and when they contract, they pull the body wall forward, increasing the length of the segment. This movement also creates a narrower body segment.
As the circular muscles lengthen the segment, the earthworm uses its setae to anchor the front of its body in the soil. This anchoring is essential for providing leverage and stability as the worm pushes forward. By having a firm grip on the soil, the earthworm can then utilise its other muscle group, the longitudinal muscles, to generate forward motion.
The coordination between the circular and longitudinal muscles is key to the earthworm's locomotion. After the circular muscles have lengthened the segment and the front setae have anchored the worm in place, the longitudinal muscles contract. This contraction makes the segment shorter and wider or causes the worm to bend from side to side. As the longitudinal muscles contract, they work in tandem with the anchored setae to pull the rest of the worm's body forward.
In summary, earthworms use their circular muscles to lengthen their bodies and create a grip with their setae. This lengthening and anchoring mechanism sets the stage for the subsequent contraction of the longitudinal muscles, which, in conjunction with the rear setae, propel the worm forward. This coordinated muscle movement allows earthworms to efficiently navigate through their underground environment.
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Frequently asked questions
Worms have two types of muscles: circular muscles and longitudinal muscles.
Circular muscles loop around each segment of the worm's body. When these muscles contract, the worm stretches and becomes longer and thinner. Longitudinal muscles, on the other hand, run along the length of the worm's body. When they contract, the worm becomes shorter and wider or bends from side to side, allowing it to move forward.
Earthworms use their circular muscles to lengthen and push themselves forward. They then use their setae, which are small bristles, to anchor the front of their body in the soil. Next, the longitudinal muscles contract, making the worm shorter and wider, and pulling the rest of its body forward.
No, different types of worms have variations in their muscle structure. For example, roundworms have longitudinal muscles but lack circular muscles. Nematodes, another type of worm, also only have longitudinal muscles, which gives them their characteristic thrashing movement.
